1. Field of the Invention
The present invention generally relates to a two-way clutch and, more particularly, to a dual-mode two-way clutch that can be used in a physical mechanism wherein mechanical component parts although incapable of freely rotating in any one of first and second directions opposite to each other under a normal condition can be rendered freely rotatable in any one of the first and second directions when the necessity arises. The present invention also relates to an automobile seat back adjustment and a bearing, both having the dual-mode two-way clutch incorporated therein and
2. Description of the Prior Art
Wheels used in, for example, a cart or sliding door can, unless forcibly halted by any means, rotate along a slope under the influence of a horizontal component of force and/or an inertia force. For this reason, depending on the application, it is a current practice to use a brake mechanism to apply an external force to at least one of the wheels to halt it to thereby secure a safety factor.
FIG. 28 illustrates an exemplary construction of a one-way clutch well known to those skilled in the art. The one-way clutch shown therein comprises a shaft 81, an outer race 82, a plurality of rollers 83, a retainer 84 and a plurality of springs 85. The outer race 82 has an inner peripheral surface formed with inclined cam faces 86 equal in number to the number of the rollers 83, and the springs 85 are used to urge the associated rollers 83 towards respective narrow regions of the cam faces 86 so that when and so long as the shaft 81 is locked in position, the outer race 82 is inhibited from rotating in a clockwise direction as viewed therein.
An exemplary construction of a two-way clutch known to those skilled in the art is shown in FIG. 29. This two-way clutch shown therein comprises a shaft 91, an outer race 92 positioned radially outwardly of the shaft 91 and a plurality of rollers 93 interposed between the shaft 91 and the 92. The structure so far described is substantially similar to the one-way clutch, but the two-way clutch is generally characterized in that the outer race 92 has its inner peripheral surface formed with two mutually opposed cam faces 97 for each of the rollers 93, in that two springs 95 and 96 are positioned on respective sides of each of the rollers 93 and in that a means, for example, a lever 98 in the illustrated example, is provided to displace a retainer 94 in a direction circumferentially of the shaft 91. This exemplary two-way clutch shown in FIG. 29 has a function of switching a direction in which the outer race 92 is locked in one of clockwise and counterclockwise directions by causing a circumferential displacement of the retainer 94 to bring each of the rollers 93 to a position engageable with one of the respective cam faces 97.
As the nomenclature indicates, the one-way clutch can lock rotation in one direction. On the contrary, the two-way clutch although having a function of locking selectively in one of the clockwise and counterclockwise directions depending on manipulation of the lever or the like, has no function of locking rotation in both directions. Accordingly, the both cannot be effectively utilized in association with the wheels of the cart or the sliding door which requires a high safety factor.
When it comes to a manually adjustable reclining seat assembly currently employed in automotive vehicles, the mainstream is the use of a ratchet mechanism, although some of the manually adjustable reclining seat assemblies make use of a planetary gear mechanism, for adjustably repositioning the seat back relative to the seat. However, the use of the ratchet mechanism permits the seat back to be adjustable stepwise relative to the seat and has therefore been found posing a problem associated with the convenience to use. The use of the ratchet mechanism has an additional problem in that when the seat back is folded down or erected relative to the seat, obnoxious sounds tend to be generated as a result of incomplete engagement of toothed component parts.
On the other hand, although the planetary gear mechanism permits the seat back to be continuously adjusted relative to the seat, not only can the seat back adjustment be manipulated in a one-touch fashion, but the structure is complicated enough to make the planetary gear mechanism expensive and costly.
In either case, the conventionally utilized seat back adjustment for automobile use generally has a problem in that if the seat back is excessively folded down or erected, the seat back must be repositioned by manipulating an adjustment lever, involving an insufficient operativity.